The B-17C was the first version of the Flying Fortress to be used in combat, as the RAF Fortress I. This experience began to suggest that the Flying Fortress was not combat ready in its current form and would lead to the development of the much more heavily armed B-17E.
All of the gun positions of the B-17C saw some change from the B-17B. The earlier aircraft had carried a single forward firing machine gun and four single guns in gun blisters around the fuselage. On the B-17C the gun blisters were all removed. The side blisters were replaced by teardrop shaped windows that had to be opened to allow the guns to fire. The lower gun blister was replaced by an armoured “gun tub”, carrying a single gun that could fire down or behind the aircraft. The top gun blister was replaced by a sliding Plexiglas cover that could be pulled back to uncover the gun. All four of these guns were increased in size from .30in to .50in. Finally a number of extra mounting positions were added for the .30in nose gun, including two on the side of the nose.
Boeing received a contract for 80 B-17Cs. The first aircraft flew on 21 July 1940 and the last was ready in November. 38 of the 80 aircraft were produced as B-17Cs, and the remaining aircraft as B-17Ds. Of the 38 B-17Cs produced, 20 went to the RAF, where they were given the designation Fortress I.
The RAF began to use the Fortress I over Europe from July 1941. These early sorties revealed a number of problems with the aircraft, the most important of which was that German fighter aircraft could already reach the same altitudes as the B-17. The B-17C turned out to be under-armed and under-armoured to fight off the Bf 109. It also lacked self-sealing fuel tanks, already seen as essential in combat over Western Europe. Some of these problems would be addressed in the B-17D and the B-17E, but the vulnerability to German fighters would only be solved by the appearance of long range escort fighters.
Engine: Four Wright Cyclone R-1820-65
Horsepower: 1,200hp each
Span: 103ft 9in
Length: 67ft 11in
Empty Weight: 30,600lb
Design Weight: 38.320lb
Maximum Loaded: 49,650lb
Max Speed: 323mph
Cruising Speed: 250mph
Range: 3,400 miles
Armament: One 7.62 or 7.70mm machine gun in nose, one 12.7mm machine gun in each waist window, one 12.7mm machine guns in dorsal and ventral positions
Bomb load: 4,800lb